1. Field of the Invention
The present invention relates to in plane switching liquid crystal displays, and particularly to an in plane switching liquid crystal display which can provide uniform viewing performance at different viewing angles.
2. General Background
Liquid crystal displays (LCDs) are typically used as the information display in various devices such as computers and vehicle and airplane instrumentation. One type of LCD called the twisted nematic liquid crystal display (TN-LCD) often has the drawback of a narrow range of viewing angles. Thus an improved design called the in plane switching liquid crystal display (IPS-LCD) has been developed in order to provide a broad range of viewing angles. The IPS-LCD typically has a plurality of common electrodes and a plurality of pixel electrodes all disposed on a same substrate of two opposite substrates, for driving liquid crystal molecules contained in a liquid crystal layer between the two substrates The resulting electric field is substantially planar and parallel to surfaces of both substrates. The IPS-LCD typically has a broad range of viewing angles.
According to the particular electrode array of its pixel electrodes and common electrodes, an IPS-LCD is classified as a single-domain type or a two-domain type. FIG. 7 is a top plan view showing an electrode array of a pixel area of a conventional single-domain IPS-LCD 1. Two parallel gate lines 11 are orthogonal to two parallel data lines 12, thereby defining the rectangular pixel area. A thin film transistor 16, a plurality of common electrodes 141, and a plurality of pixel electrodes 151 are formed in the pixel area. The common electrodes 141 and the pixel electrodes 151 are strip-shaped, and are arranged parallel to each other in alternating fashion. When a voltage is applied to the common electrodes 141 and the pixel electrodes 151, a horizontal electric field is produced therebetween. Long axes of the liquid crystal molecules are aligned parallel to the direction of the electric field. As a result, an amount of light passing through a liquid crystal layer (not shown) to display images can be controlled.
However, the conventional single-domain type IPS-LCD 1 has the following problem. Since the common electrodes 141 and the pixel electrodes 151 are all strip-shaped, the electric field is distributed along one direction only. When the displayed image is viewed at different oblique angles, an observer can frequently notice a quite large color shift.
In order to solve the above-mentioned problem, the two-domain type IPS-LCD has been developed. FIG. 8 is a top plan view showing an electrode array of a pixel area of a conventional two-domain type IPS-LCD 10. Common electrodes 142 and pixel electrodes 152 are designed to have a bent shape in the pixel area. Referring to FIG. 9, when no voltage is applied to the common electrodes 142 and the pixel electrodes 152, the liquid crystal molecules are aligned along a direction A. When a voltage is applied to the common electrodes 142 and the pixel electrodes 152, two electric fields E10 and E20 having two different directions are generated between the pixel electrodes 152 and the common electrodes 142. Accordingly, liquid crystal molecules are rotated in two different directions to form two light transmission regions in the one pixel area. The IPS-LCD 10 exhibits a two-domain display effect. As a result, different colors can be seen in the two regions when the display screen is obliquely viewed. Since the colors compensate for each other, the color shift in the two-domain type IPS-LCD 10 is reduced.
However, the two-domain electrode configuration of the IPS-LCD 10 still inherently limits the display thereof. Even better visual performance at various different viewing angles is desired.
What is needed, therefore, is an IPS-LCD which has fine viewing characteristics in different viewing directions.